Process and equipment for forming and treating calcium carbonate precipitates



Apnl 12, 1966 R. H. VAN NOTE 3,245,834

PROCESS AND EQUIPMENT FOR FORMING AND TREATING CALCIUM CARBONATE PRECIPITATES Original Filed March 23, 1959 5 Sheets-Sheet 1 @am 2794/@ pesa/1 uogpvaa uy ,vanaaf spy/o9 :035,3 o sausjmsppanq: aiyyas @ff/Q April l2, 1966 R, H, VAN NOTE 3,245,834

PROCESS AND EQUIPMENT FOR FORMING AND TREATING CALCIUM CARBONATE PRECIPITATES Original Filed March 23, 1959 5 Shee'cS-Sheel'I 2 IN V EN TOR.

R. H.' VAN NOTE UIPME Aprilllz, 1966 3,245,834 PROCESS AND EQ NT Foa FORMING AND TREATING CALCIUM CAR BONATE PRECIPITATES 5 Sheaets-Shee'i*I 3 Original Filed March 23, 1959 Ala/)Mre C00 n K Z@ AC PM] d D J INVENTOR. Pobe// Van/Vole BY /I/a/an; 25H

@ffy

R. H. VAN NOTE 3,245,834 PROCESS AND EQUIPMENT FOR FORMING AND TREATING 5 Sheets-Sheet 4 April l2, 1966 CALCIUM CARBONATE PRECIPITATES Original Filed March 23, 1959 April 12, 1966 R. H. VAN NOTE PROCESS AND EQUIPMENT FOR FORMING AND TREATING CALCIUM CARBONATE PRECIPITATES Original Filed March 23, 1959 5 Sheets-Sheet 5 INVENTOR.

ROBERT H. VAN NOTE BY www 2%@ ATTORNEY.

United States Patent() PROCES AND EQUEPMENT FOR FRMING AND TREATING CALCIUM @ADN ATE PRECIPI- TATES Robert H. Van Note, Westport, Conn., assigner to porr- @liver incorporated, Stamford, Conn., a corporation of Delaware y j Original application Mar. 23, 1959, Ser. No. 801,161, 110W Patent No. 3,089,789, dated May 14, 1963. Divided and this application Nov. 26, 1962, Ser. No. 247,781

13 Claims. (Cl. 127-12) This application is a division of application Serial No. 801,161 filed March 23, 1959, now Patent No. 3,089,789.

This invention relates to the discovery that calcium carbonate reaction precipitate (CaCO3) at solids concentrations of 50 to 70 grams per liter of mother liquor has improved settling characteristics, i.e. readily settled, thickened and filtered. More particularly, this invention relates to the formation of CaCO3 precipitate in the presence of active CaCO3 seed or primer to form a solids suspension of CaCO3 particles (comprising seed material and CaCO3 reaction precipitate) within the range 50-70 grams per liter of mother liquor.

An active CaCO3 precipitate is defined "as freshly precipitated CaCO3 as distinct from Whiting Active CaCO3 seed or primer may be precipitate from a previous operation, or separately prepared, and may also be ob-V tained by progressive additions of carbonateto a solution of limed mother liquor wherein the previous reaction precipitate becomes the seed or nuclei for the next successive carbonation such as disclosed in U.S. Patent No. 2,557,800.

The precise phenomena responsible for the high settling rate, thickening concentrations and iilterability of'CaCOB particles within the range of 50 to 70 grams per liter, particularly those formed by seeding is not completely understood. It is believed that the improvements in settling characteristics of active CaCO3 precipitate (normally formed as very fine particles which are characteristically difiicult to settle, thicken and filter) is due to increasing the rate of reaction, or driving force for the reaction, by Which the precipitate is formed. Increasing the rate of reaction, or forming quickly settling reaction products, is provided by supplying an optimum quantity of active CaCO3 seed or nuclei, with which the reactionprecipitate-coagulates, fiocculates or agglomerates, to form relatively large particles'. That is, the nucleihastens the formation of reaction-precipitate with which it also forms a relatively large particle to quickly settle and thicken the reaction precipitate to high concentrations. Accordingly, I have discovered that a maximum rate of reaction for CaCO3 is obtained at 50 to 70 g.p.l.

This invention has utility in any art where it is desired to separate CaCO3 reaction-precipitate from the mother liquor by sedimentation clarification, thickening or filtering. For instance, it can be used in the purification of sugar juice, including beet sugar juice, in water softening,

or brine processing, and in the production of White liquor by causticizing green liquor in the art of processing paper ulp. y p While the literature on sugar juice purification by liming and carbonating presents a very great number of different processes, whatever the process used, it is inevitable that after liming or def-ecation (the chief function of which is destructive reaction), CaCO3 must be precipitated with carbonio acid or CO2y to remove impurities. Therefore, while this invention relates most particularly to the carbonation step in limingand carbonating processes for purifying sugar juices, it will also favorably influence the step of pre-liming sugar juice sothat impurities precipitated with CaO can be readily removed prior to carbonation as hereinafter fully disclosed.

A furtherl feature of this invention is a system for automatically maintaining a 50 to 70 g.p.l. reaction product in a continuous carbonation vessel. Briefiy, this system provides control of the'quantity of CaCO3 sludge removed from a carbonation thickener i.e. multi-tray sedimentation thickener or a filter, and supplied to a mixing tank containing the juice to be carbonated, regardless of the density of the thickener sludge. That is, the quantity of CaCO3 recycle willy be maintained substantially constant even though the density of the sludge or filter c'ake' may vary radically.

Also forming a part of this invention is a preferred apparatus for carrying out the above-described carbonation process. This apparatus consists essentially of a carbonator-reaction tower in which the juice is subjected to carbonation in one pass through the reactor. Prior art carbonators, exemplified by the Diorr and Benning Car# bonators, recycled previously carbonated juice back yto the reaction vessel together with incoming diffusion'juice;

Therefore, a primary object of this invention is to pro vide a process for the production rof readily thickened, settled, and filterable CaCO3 precipitate.

A further primary lobject of this invention is to provide a continuous sugar juice purification system having greater economies and e'fiiciencies than heretofore whileproducing maximum quality carbonate juice with respect to purity, color, and lime salts content.

Another primary object of this invent-ion is to provide a one pass carbonation method and apparatus for continu ous carbonation of sugar juice.

A further object of this invention is to provide a system particularly suited to carrying out the primary objects of this invention in relation to beet sugar processing.

Another object of this invention is to provide an improved sugar purification process by Which increased capacity 'of clarifiers, thickeners, washers, andfilter appa-l ratus is obtained as a result of improved settling, thickening and filtering characteristics of CaCO3r precipitate according to this invention.

A further advantage of the process of this invention resides in reduced settling and thickening area requirements, with the resultant advantage that smaller, less expensive sedimentation thickene'rs and filters can beA used in sugarproduction. The advantage of reduced detention time in such apparatus results in greater yieldl and greaterl impurity eliminations from sugar juice. y

Another significant object of this invention is maximum utilization of the improved decantation thickening and filtering characteristics of CaCO3 solids formed or produced A,at 50-70 y g.p.l. vIn a sugar juice purification process, the improved CaCO3 solids are not only utilized as seed material for the carbonation step but are also utilized in the pre-liming step to produce a high quality, pre-limed juice from which most of the impurities have been removed. According tothis feature of the invention, CaCO3 produced at 50-70 g.p.lv. in the sugarY carbonator is thickened and recycled to the prelimer step so that pre-liming is carried out in Vthev presence of these" solids and efliuent from the prelimer is decanted whereby the settling, thickening and filtering properties of the recycled CaCO3 makes it possible to readily remove irnpurities from the prelimed juice prior to carbonation thereof. In this way, the juice whichis tofbe carbonated' is relatively pure and as a result firstrcarbonate juice is of high quality. Also a relatively clean CaCO is producedy which readily coagulates, agglomerates or fluocculates with the precipitate formed during the preliming step and the carbonation step of a sugar purification process. Therefore, it will be understood from the foregoing that this invention relates to improving the over-all process of treating sugar bearing juice.

Another feature and object of this invention is a continuous beet sugar purification system in which a quantity of solids is removed from the first carbonation stage (sedimentation-thickener-sludge or filter cake) which is substantially equal to the quantity of solids present in the carbonator upon completion of the reaction between CaO and CO2. This quantity of solids is split into one portion which is recycled to the carbonator to obtain a solids concentration of 50-70 g.p.l. upon substantial cornpletion of the reaction of CaO and CO2 therein. The remainder of the quantity of solids removed from the carbonator is delivered to a prelimer stage and subsequently removed in a prelime-separator, preferably a sedimentation thickener. The recycled solids in the prelimer act as an aid to sedimentation and filtration of prelime precipitate.

' Other objects and advantages together with the foregoing, will be more readily understood from the following detailed descriptions taken with the drawings in which:

FIG. 1 is a graphical illustration of the relationship between settling rates of CaCO3 solids formed in a reaction vessel at various solids concentrations.

FIG. 2 is similar to FIG. 1 and illustrates the relationship between thickening and filtering characteristics of CaCO3 precipitate formed in a reaction vessel at various solids concentrations.

With regard to FIGS. 1 and 2, it is noted that the curve shown therein relates the solids concentration in a reaction vessel (axis of abscissas) to the settling, thickening and filtering characteristic of the reaction contents in a sedimentation thickener (axis of ordinates). The concentration of CaCO3 Within the reactor, upon substantial completion of reaction, is settled and thickened to obtain the curves shown in these figures. Also, the curves of FIGS. 1 and 2 were obtained by having active CaCO3 seed material present during the reaction forming precipitated CaCO3. FIG. 3, curve A is a graphical illustration of the advantages or results obtained by this invention in the area requirements necessary to settle and thicken CaCO3 solids. Curve B shows these results as related to beet sugar processing in terms of tons of beets/ day.

FIGS. 4 and 5 are schematic fiowsheets illustrating an improved sugar juice purification process embodying the teachings of this invention.

' FIGS. 6 and 7 are elevational schematic views of a control system for recycling material to accomplish the objectives of this invention in the owsheets of FIGS. 4 and 5. v

FIGS. 8 and 9 are elevational schematic views of a low detention time, one pass carbonator.

FIG. 10 shows the carbonator of FIG. 8, enlarged and more fully executed; FIG. 11 is a cross-sectional view taken on line 11-11 in FIG. 10.

Referring to the drawings, FIGS. 1 and 2 graphically illustrate that maximum settling rates and thickening concentrations for CaCO3 precipitate .are obtained at concentrations within the range of 50-70 g.p,l. However, a's previously stated, a 50'to 70 g.p.l. concentration obtained by forming CaCO3 precipitate in the presence of active CaCO3 results in the greatest possible settling and thickening characteristic. Therefore, the axis of abscissas of FIGS. 1 and 2 are the concentrations of solids within the reactor which are fed to a sedimentation vessel, upon substantial completion of reaction.

With reference to FIG. 2 it is noted that the filterability of CaCO3 is proportional to the concentration of thickened CaCO3. Thus, FIG. 2 also illustrates that maximum filterability of CaCO3 is also obtained at 50 to 70 g.p.l. reactor concentrations.

Another advantage obtained by this invention, in terms of thickening area requirements, is illustrated in FIG. 3.

Curve A of FIG. 3 depicts the unit thickening area requirements for CaCO3 solids formed in the presence of previously precipitated CaCO3 or seed. The solids concentration of the suspension being varied, either by changes in the solids concentration of the newly formed precipitate, or the quantity of CaCOa seed present during the formation of the new precipitate. Both alkalinity and underflow solids concentrations within the sedimentation thickener are held constant over the entire solids concentration range. v

Unit thickening area by definition is the cross-sectional area required to thicken one ton of solids per day from a feed solids concentration to an underflow solids concentration, and is usually expressed in terms of sq. ft. thickening area per ton of solids per day.

Curve A of FIG. 3 shows that unit area requirements are reduced as the concentration of solids increases. However, the reduction in thickening area requirement is not a linear function with respect to solids concentration, since the rate of change becomes less pronounced as solids concentration increases. The physical characteristics of the newly formed and seed solids are identical in every respect as long as some of the seed solids are present during reaction of the chemical constituents which form the new precipitate solids. In other words, regardless of the ratio between new solids formed and seed solids, thickening larea requirements will be essentially those depicted in FIG. 3, curve A. That is, thickening area requirements change as the total solids concentration in the reaction vessel is changed. Curve A by itself would suggest that greater solids handling capacities could be gained in thickening apparatus as solids concentration of the feed is increased to infinity. However, optimum thickening conditions are achieved within a total CaCO3 solids concentration range of 50-70 g.p.l. It is true that thickening area requirements decrease with a continual increase in solids concentration in the reaction vessel, but the quantity of total solids per unit volume also increases. As a result, thickening apparatus handling a CaCO3 suspension reaches its maximum capacity when the feed suspension and solids concentration present in the reaction vessel is within the range of 50-70 g.p.l. In the light of the foregoing, it will be seen in sugar juice purication, for example, that only the quantity of lime required to effect maximum purification need be added since an optimum quantity of CaCO3 solids can be recycled to produce maximum settling, thickening, and filtration of the sludge. In this way, lime addition is held to a minimum resulting in an overall savings in the juice purification process.

Curve B, FIG. 3, depicts the phenomena illustrated by curve A for the case of beet sugar juice purification. In this case, unit thickening area requirements are given in terms of the raw material processed; that is, sq ft. thickening area per ton beets processed per day. Similar curves could be developed showing unit thickening area requirements based on unit weights or volumes of the finished product; that is, on tons of carbonated juice per day, gallons per minute of carbonated juice, etc. However, since most calculations in the sugar industry are reduced to a beet capacity ratio, the units of measurement given (ft.2/ ton beets/day) are preferred.

It may be shown that the following formula relates unit thickening area requirements, U.A.S, in terms of ft.2/ ton solids/ day to thickening area requirements U.A.B, in terms ft2/ton beets/ day.

U.A.B= U.A.S XCO X 100089.

Where: CO is the CaCO3 solids concentration in terms of gms./li ter; s.g. is the specific gravity of the juice assumed s.g.-l.06 gms/cc.; d=draft, assumed d=1.26;

-tb/a=ton beets/day. By definition of unit"thickening area, ton beets/day is unity, therefore (1) becomes:

U.A.B=.00l 19 UJI .SX CO Substituting points from Curve A, FIG. 3 into Equation 2, we have:

oo U.A.S U.A.B

2o 1s. 0 0. 42s so s. 6 0. 307 40 4. s k0.219 o 2. s 0. 167 so 2. 3 o. 164 70 2. 1 Y 0.175 so 2; o o. 1go 90 1. 9 o. 204

CaO on beets would be operating with gms/liter y CaCO3 solids in the carbonator. Under these conditions, 0.307 ft2 thickening area would be required to handle the juice from each ton beet processed per day. Under the same conditions but with recycling sufcient sludge to increase the CaCO3 solids concentration in the carbonator to 60 gms/liter, the same quantity of juice could be processed in 53.5% `of the thickening area. lFurther increase of the solids concentration in the carbonator to 90 gms/liter, by recycling more solids, would increase thickening area requirements by 24.4% over that optimum for the system. Thus, by practicing the art of sludge recycling within a range such that -70 gms/liter CaCO3 solids concentration is maintained within the reaction vessel, thickening apparatus is held to a minimum, thus reducing machine and installation costs. As an added advantage, iin sugar juice processing, Ithis also reduces detention time in the process, thereby reducing juice degradation to a minimum.

Thickening area requirement will vary depending upon juice alkalinity, underflow solids concentrations, specific gravity of the juice, factory draft, and the nature andl condition of the beets. All of these variables will tend to shift curve B, FIG. 3 vertically up or down. Regardless of these variables, however, the specified solids concentration range of 50-70 gms/liter would be 0ptimum for all operating conditions. and curves could be drawn for brine purification, water treatment, recausticizing, and the like where CaCO3 solids are precipitated and thickened. While units of measurement of thickening area requirements would normally be in gallons per minute of brine, water, and white liquor processed, with actual values being dependent upon variables inherent in each industry, the general shape of the curve would be identical to that of curve B, and maximum capacities would be achieved by maintaining a CaCO3 solids concentration of 50-70 gms/liter in the reaction vessel.

In the case of brine purification and water treatment, vas in beet and cane juice purication, normal solids concentration in the reaction vessel and therefore, ythe feed concentration to a sedimentation tank are lower than the specified optimum solids concentration range. In these cases, then, solids must be recycled to the reaction vessel to maintain the proper solids concentration.

On the other hand, in the precipitation of CaCO3 in the production of white liquor in the recausticizing field, Vsolids concentration in the recausticizers are 'greater than the optimum range. In this case, the invention teachers recycling a sufficient quantity of white liquor back to the recausticizers such that a solid concentration range of This curve gives the I* Similar calculations S0-70 gms/liter solids is maintained and fed to the sedimentation tank.

With regard to sugar juice carbonation, the alkalinity of the solutions represented bythe graphs shown in FIGS. 1, 2 and 3 is the same as normally associated with rst carbonation (approximately 0/ 1% on beets).

The owsheet of FIG. 4 illustrates a process for extracting sugar from beets employing the rst carbonation teaching according to this invention and utilizing this teaching to favorably influence; (a) preliming of the diffusion juice, (b) clarification of prelimed juice, (c) clarification of the rst carbonation juice, and (d) minimizing the detention time of the juice from its introduction into the prelimer through lthe various stages of treatment until the juice appears as clarified rst carbonation lju1ce.

In the embodiment according to FIG. 4, diffusion juice is introduced into prelimer 1 which is preferably, but not necessarily, of the type known as the Brieghel-Muller Prelimer (U.S. Patent No. 2,610,929). A Brieghel- Muller Prelimer consists essentially of an oblong tank with a semi-circular bottom. The lower or bottom half of the tank is partitioned into a number of cells. A shaft passing through these cells carries stirring arms and paddles located in each cell for mixing the liquid. Above the cells, each partition carries a shaft extending upwards from its center and each of these shafts carries an oblong shutter device of a width equal to that of the tank. Beet juice enters at the top of one end of the tank and leaves from the bottom of the other end of the tank Via a constant level overflow pipe extending upwards from the bottom of the last cell. Lime is introduced in the top of the last cell (limed juice exit) and stirrer arms tend to push the liquid from the liming end of the juice inlet end of the tank; the flow through the tank being controlled by the shutters. A degree of mixing juice and lime can thus vbe achieved whereby constant alkalinity can be maintained in each cell. Milk of lime is gradually added to the prelimer over a period of 15-20 minutes in accordance with the teachings DEDEK-VASATKO as disclosed in U.S. Patent 2,007,424. According to the DEDEK-VASATKO preliming practice, an optimum quantity of lime is added to a continuously stirred, heated diffusion juice, the lime being added first in small quantities until 0.3 to 0.5 CaO has been added over a period of 15-20 minutes, and the remainder being then added all at once. Carbonated sludge yfrom a carbonation thickener 6 is also introduced into the prelimer, at the juice inlet end thereof, for the purpose of stabilizing the juice as disclosed by BrieghelMuller, U.S. Patent 2,697,049. It is noted that the flowsheet of FIG. 4 is distinct from the Brieghel-Muller stabilization concept in that only the solids which are insoluble with CaO are recycled to the prelimer. That is, in the Brieghel-Muller stabilization concept limed diffusion juice is carbonated without rst removing non-sugar solids which are rendered insoluble with CaO. Therefore, the recycled sludge from the carbonation thickener has all the impurities contained in the diffusion juice. According to the owsheet of FIG. 4, al1 the impurities insoluble with CaO are removed from juice by the prelime thickener 2. As a result, solids recycled to the prelimer, kaccording to this invention, is relatively clean ACaCGj.

A fur-ther distinction between the owsheet of FIG. 4 and prior art practices, including Brieghel-Muller stabiliz'ation, is as follows:

Sludge recycled from the carbonation thickener '6 'to the prelimer is not returned to the'carbonator 5 and .thence returned to the carbonator thickener 6. The recycled sludge, according to FIG. 4, is removed from a system by thickener 2 prior to carbonation thus preventing impurities going back into solution in main-liming and/ or carbonation to increase the color and decrease purity of the rst carbonation juice overflowing from thickener 6. Also, the recirculating load is minimized because it is withdrawn from the system close to its point of introdxmtion.

The stabilized, prelimed dilusion juice is conducted to a prelime-sedimentation-thickener 2 of the multi-tray type, to remove non-sugars rendered insoluble by CaO.. Recycled CaCO?l aids settling of non-sugar impurities: entering thickener 2. Underflow from thickener 2 is iiltered at 3 wherein the recycled CaCO3 now acts as ay filter aid to facilitate separation of the otherwise slimy, dicult to filter solids, formed by non-sugar impurities rendered insoluble by CaO. Filtrate from filter 3 is used to slake-lirne and produce CaO as is well-known.

Clarified prelimed juice overliowing thickener 2 is mixed with the relatively clean CaCO3 sludge from carbonationvthickener 6, together with main-lime CaO (normally in the range of 1.5 to 2.25 CaO on beets). Preferably, mainliming is accomplished just before or substantially simultaneous with the introduction of CO2. The quantity of recycled CaOO3 is determined by the quantity of CaCO3 to be precipitated in vessel by reacting CaO and CO2. Generally, the quantity of C-aO and CO2, and therefore, CaCO3 precipitate produced by this reaction is determined by the qu-ality of the beets to be processed as is weilknown. Therefore, the quantity of recycled sludge entering mix tank 4 must be equal lto the quantity of solids necessary to obtain 50-70 g.p.l. upon substantial completion of reaction in vessel 5. For example, if CaO and CO2 introduced to reactor 5 will produce `30 g.p.l. reaction CaCOa then 20 t-o 40 gpl. recycled CaCO3 is dcjlivered to mix tank 4. As Ia result a 50 to 70 g.p.l. solids:

suspension is obtained in reactor 5 upon completion of the reaction which is conducted, at this concentration; range, to a carbonation-thickener 6. Therefore, the suspension entering thickener 6 at 50 to 70 g.p.l. obtains optimum decantation and thickening with minimum detention. Further, it is well-known that improved juice qu-ality can be obtained at high alkalinities but at =high alkalinties it is diiiicult to separate the precipitates from the juice. Due t-o the improved decantation and filtering characteristics of CaCO3 produced at 50-70 g.p.l. as herelinabove described, it is now possible, as a practical matter, to utilize high alkalinities of pre-limed and first carbonate juice without experiencing difficulties with separation of the solids from said juice.

Carbonator 5 may be of the well-known Benningor Dorr ty-pe but is preferably of the one pass, low detention type carbonator shown in FIGS. 8 and 9.

As shown in FIG. 4, a mix-tank density controlle-r 9 regulates the capacity of pump 8 to maintain constant a predetermined ratio of juice to CaCO3 seed material within the tank 4. The density controller is manually variable to determine the juice `to seed ratio according to the quality and quant-ity of beets being processed and other known variables. The density control system 9 may be of any known type which pneumatically, electrically or mechanically v-aries the opening of a valve or the capacity of a positive displacement pump. A system suitable for use as a density controller 9 is disclosed in FIG. 6 and FIG. 7 hereinafter described.

To prevent recycling carbonated juice .and have an available source of CaCO3 seed material for the carbonator and/ or prelimer, it is necessary to maintain a sludge reserve or inventory within .the carbonation-thickener 6. Once the 4thickened sludge builds u-p within the bottom of the thickener 6, it is maintained at a predetermined level by Ia sludge inventory control 10 which regulates or controls .the capacity of pump 7. Pump 7 and associ-ated conduits deliver sludge from thickener 6 to the prelimer 1. As a result, once a sludge inventory has been established during start-up, the inventory 10 and pump 7 maintain this inventory by removing only an amount of solids equal to the newly formed solids transferred to thickener `6 from carbonator 5.

As a result of the action of control 9 and pump 8, a solid suspension'upon completion of reaction within the carbonator S will be maintained within the 50-70 g.p.l.

range. It will be observed that by this arrangement, a

supply of sludge for recycle to mix-tank 4, and/or to the carbonator 5, is insured by the operation of the inventory control 10 which will reduce the capacity of pump 7 before the sludge required by fthe carbonator can be depleted. However, when starting up operations have been completed, the quantity of solids sent .to the prelimer 1 by pump 7 is substantially equa-l to the amount of solids entering the thickener 6, less the sludge required by mix- @tank 4 as determined by the density controller 9 and pump 48 controlled thereby.

FIG. 5 shows a flowsheet differing from How-sheet of FIG. 4 in that a rotary d rurn iilter 6a replaces the sedi- .mentation unit 6 of FIG. 4. vAsshown in FIG. 5, carbonated juice and the solids suspended therein are fed to a rotary drum Aiilter 6a where the solids are separated -from the first carbonated juice reporting as filtrate. The ilter cake is discharged from the drum in the usual man- :ner and is preferably transferred to a mix-tank 1-1 to be lreslurried with clarified predefecation juice 11a from thickener 2. Reslurried iilter .cake is pumped to a mixltank 4 as above described by a pump 8 which is controlled by a mix-tank controller 9. Pump 7 transfers the remain- ;ing filter cake suspension from the tank 11 back to the @prelimer as heretofore disclosed. Pump 7, in Ithis arrangement, can be regulated 4according to the position of a float yin tank 11 or in suitable known manner. Alternatively carbonated juice 11b from reactor 5 may be used :to reslurry the lter cake or the ilter cake may be recycled wi-thout reslurring if desirable.

Examples of maintaining correct balance of solids concentration at carbonation station by the recycle 0f thickener underow Example 1.-A factory slicing 3000 ltons .beets/day having a draft of 1.30 uses 1.5% CaO on beets.

Raw juice flow:

tb da 3000 ZTX 14.40 min.

2000# Ton juice gal. 8.84#

1.30 ton juice tb Lime used:

2000 3000 .015 XTO-Z Cao/mln.

CaCO3 produced:

62.5X5"=1l1.5 i# 03003/111111.

CaCO3 concentration:

111.5# 615 gah-'181 gal.

It is desired to have a solids concentration of 50-70 gms./ liter CaCO3 solids .at the carbonation station:

Say:

60 gms. 60 gms. 3.785 litery 0 0 Liter Liter gal. 454 gms* gal.

of raw juice. Present standard continuous carbonation means recycle a quantity of carbonated juice` equivalent to 70D-900% of raw juice while producing solids which require greater thickener capacity to separate.

Since considerably less quantities finished Ifirst carbonation juice are recycled, degradation of the juice going :to further processing is held to a minimum.

Example 2.--Conditions equal to those of Example 1 except that 2.25% CaO on beets is used.

Raw juice ow: `615 gpm. Lime used:

CaCO3 produced: 94.0X100=168 CaCOa/min. CaCO3 concentration:

0.500-0.'274=0.226 gal. CaCO3 should be recycled lin the form of thickener underliow.

0.226 )4615*:139 #/min. CaCO3 recycle.

Ratio of recycled `CaCO3 to new CaCO3 equal to 0.8-3zl.

Assuming 2.50 lif'/ gal. CaCO3 in underiiow.

`139/2.5O 55.7 gal/min. underliow recycled,

v55.7-139/'225--495 gals. of juice recycled.

49.5/615X100-f8.1% of raw juice recycled.

A further discovery according to this invention as illustrated in FIGS. 4 & 5 relates to the temperatures at which the juice is prelimed and carbonated. lIt is known in the sugar industry that juice temperatures effect both decantation :and/or tilt-ration as well as juice quality. At high temperatures (approximately 95 C.) a poorer quality juice is produced than at lower temperatures (approximately `55 C.). However, the high temperatures are used used because it is commercially impractical to separate the solids at the low temperatures. Due to the improved decantation and filtration of CaCOa produced in a carbonator at 50-70 g.p.l., it is now feasible to use low temperatures in sugar production for selective removal of impurities.

A pilot plant utilizing the owsheet as given in FIG. 4 was operated experimentally at a U.S. beet sugar fac tory. The invention of maintaining a calcium carbonate solids concentration of 50-70 g.p.l. in a single pass carbonator was practiced. Factory operation consisted of (1) carbonating the diffusion juice in a standard Dorrtype carbonator with 700% recirculation of treated juice at temperatures of 70-80 C. (2) Splitting the juice after carbonation into two streams; one stream being -tiltered on Kelly filters, the other stream clarified in a Dorr thickener.

Samples were collected of the pilot plant eiiiuent, the LKelley filter filtrate, and the Dorr thickener overflow. These samples were -analyzed by standard laboratory methods to determine the apparent purity, color and saponin content of each. Because of the variance within each set of d-ata, statistical methods were employed to determine if the differences in the averages between any two sets of data were significant. In this type of work, differences are assumed statistically significant when condence levels of 95% or greater are reached. At a 95% contidence level, odds are 19:1 that any difference found is not due to chance. An increase in the magnitude of these odds permits greater confidence in `the data.

Results `of koperation are given below. These results represent operation under controlled conditions, the only variable changed in pilot plant operation being temperature. It is shown from these results that,

(l) The lower the temperature at the preliming step Within practical limitations of factory opera-tion, the

greater is the removal of coloring matter and saponin in the process.

(2) The higher the temperature at the preliming step with practical limitations of factory operations, the greater is Ithe purity rise or total impurity removal in the process.

The two extremes in temperatures at the preliming step each favor the removal of certain impurities which are important t-o the economics of sugar making. iLoW temperature preliming selectively removes coloring matter saponin. I'Both of these two types of impurities are important to the quality of sugar produced. If either of these remain too high in concentration after c-arb-onation of the juice, the sugar produced from this Ijuice might be of inferior quality and its price on the market reduced considerably. On the other hand, high temperature preliming removes a greaterquantity of total impurities. The greater the removal of impurities through carbonation, the greater will be the recovery of crystallized sugar in subsequent processing. This greater recovery increases the total revenue gained by a sugar company ,and thus makes lthe processing of sugar more economical.

A compromise therefore must exist in choosing the correct temperature for preliming. The temperature chosen at preliming will depend upon the mode of operation and equipment used in subsequent steps in sugar processing. Hence, temperatures at preliming may range from 55 C. to C. depending upon the factory in which the process is used.

Resulls 0j pilot plant operationl compared with normal first carbonation factory operation I Low temperature preliming-Temperature maintained .at 55-60 C. during preliming and subsequent step of clarilication of prelimed juice. Thereafter, temperature increased to 70 C. during carbonation.

(a) Comparing pilot plane efliuent with direct filtration of factory irst carbonation juice using Kelly Filters'.

(l) Apparent purity: 0.28 points higher in pilot plant etiiuent. Difference was highly statistically signiiicantodds that difference was not due to chance were 40:1.

(2) Color: 14.6% less coloring matter in pilot plant effluent. Odds that difference was not due to chance were 999:1.

(3) Saponin content: 33.8% less sapon'm in pilot plant eluent. Odds that diiference was not due to chance were 99:1.

(b) Comparing pilot plant effluent with clariication of factory first carbonation juice using Dorr thickener.

(l) Apparent purity: 0.29 points higher in pilot plant ciiiuent. Odds that difference was not due. to chance were 40:1.

(2) Color: 30.2% less coloring matter in pilot plant effluent. Odds that difference was not due to chance were 999:1.

II High temperature preltming.-Temperatrue mainta-ined at 70-80 C. throughout preliming land carbonation steps of process.

(a) Comparing pilot plant effluent with direct iiltration of factory first carbonation juice u-sing Kelly lilters.

(l) Apparent purity: 0.63 points higher in pilot plant effluent. Odds that difference was not due to chance were 200:1.

(2) Color: 115% more coloring matter in pilot plant eiuent. Odds that difference was not due to chance were 200:1.

(3) No statistically signicant difference in saponin content of two juices.

(b) Comparing pilot plant efliuent with clarification of factory ii-rst carbonation juice using Dorr thickener.

(1) Apparent purity: 0.72 points higher in pilot plant eiiiuent. Odds that ditference was not due to chance were 200:1.

(2) Color: 6.9% less coloring matter in pilot plant eliuent. Odds that dilference was not due to chance were 200:1.

Vshown is substantially a one pass carbonator.

A detailed description of one type of arrangement for controlling the sludge recycle to prelimer and carbonator according to the flowsheet of FIG. 4 is illustrated in FIGS. 6 and 7. The instruments illustrated are well known stock items and therefore only a brief description thereof will be given. With reference to FIG. 6, it will be seen that Thickener 6 is provided with a stand pipe 20 communicating the thickener sludge sump with a super elevation pipe 21. Clear juice from the thickener overflow is fed to the super elevation pipe in any suitable manner. A pair of air bleed tubes Z2, having their open ends in the same horizontal plane sense the difference in density between thickener overflow and thickener underflow. This difference is sensed by la pneunratc differential pressure transmitter 23 which signals a sludge inventory recorder and pump'controller 24 whereby a sludge inventory is maintained in thickener 6. vAnessentially identical arrangement is utilized in controlling pump 8 to maintain a predetermined juice to seed ratio in mix-tank 4.

A suitable transmitter 23 and controller recorder 24 are manufactured by Taylor Instrument Corp. of Rochester, New York `and are fully described in Taylor Bulletins 98258 and 98158. A similar control system is also disclosed in U.S. Patent 2,715,463.

The Iapparatus illustrated in FIGS. 8 and 9 is a one pass carbonator particularly advantageous for carbonating beet sugar juice; In the foregoing Example 1, it was noted that present standard continuous carbonation apparatus recycled a quantity of carbonated juice equivalent to 70D-900% of the raw juice thereby considerably increasing detention time. The apparatus illustrated in FIG. 8 and enlarged and more fully executed in FIGS. and ll, and also the one illustrated in FIG. 9, decreases the percent of raw juice recycled from 700-900% to 8 to 12%. Relative to prior practices, the carbonator In FIG. 8 and FIGS. 10 and 11 respectively, like parts are designated by like numerals. Reference 30v generally designates the one pass -carbonator to which diffusion or predefecation juice is supplied by suitable piping and Where the process of this invention is utilized .active CaCO3 is mixed with the juice. CaO is added in chamber 31 and the lime juice split into substantially equal volumes to be introduced tangentially namely through respective branch pipes 32a .and 32b on opposite sides of a cylindrical mixer 3-2, adjacent the bottom of the carbonator. Mixer 32 has radially, inwardly extending flanges 3-3 which define circulating raceways 34. The juice enters the raceways at opposite sides and flows counter currently therein. The juice is displaced radially inwardly into an annular area where the liquid discharging from the raceways is intimately mixed by the eddies created upon impact of the two oppositely direct streams. CO2 is fed into this annular zone of turbulence by a circular gas port 35 between the raceways. CO2 is .fed to port 35 by a -gas line l36 and distributing header 35a. The port .35 is maintained free of scale by one or more rotating scraper blades 37 which overcomes carbonator sealing problems so that the carbonator of FIG. 8 can be run continuously without shut-down for descaling.

While the arrangement of FIG. 8 is preferred a conventional CO2 distributor 38 may al-so be utilized as shown in FIG. 8a yand FIG. 9.

The reaction between CaO and CO2 is carried out in the carbonator tower 39 during ascent'of the carbonator contents and is substantially completed before discharge into a sedimentation thickener.

Many other modifications, as well as applications of the foregoing teachings, will be -obvious to those skilled in the larts mentioned as well as others; therefore, the invention is limited only by the scope of the appended claims.

I claim:

1. Apparatus for the carbonation treatment of sugar juice by the reaction of lime with CO2, which comprises a vessel arranged for continuous upward flow of juice therethrough;

means for introducing said juice int-o said vessel, comprising at least a first and a second coaxial annular channel means in juxtaposition relative to each other and inwardly open and horizontally surrounding a mixing zone and located in the lower end portion of said vessel; feed conduit means for simultaneously feeding juice into respective channel means in respective opposite directions, whereby the directional flow energy of the countercurrent streams in said channel means is converted into random turbulence in said mixing zone;

and supply duct means for introducing CO2 into said mixing zone and arranged for delivering said CO2 substantially in the zone of mutual impact of said countercurrent streams, at the inner periphery of said channel means.

2. Apparatus according to claim 1, wherein said vessel has a bottom portion providing a pocket below said annular channel means.

3. Apparatus according to claim 1, wherein said supply means comprise a -vertical supply cond-uit leading to said mixing zone, and having laterally extending delivery branches with delivery ends thereof terminating substantially in said zone of mutual impact of said countercurrent streams.

4. Apparatus according to claim 1, wherein said supply means comprise an annular port between said rst and second annular channel means, and means for feeding CO2 into said annular port for deliveryl in said zone of mutual impact of said countercurrent streams.

5. Apparatus according to claim 1, wherein said supply means comprise an annular port between said iirst and second annular channel means, and means for feeding CO2 int-o said port for delivery in said zone of mutual impact of said countercurrent streams, .and wherein means are provided for introducing lime into said channel means.

6. Apparatus .according to claim 1, wherein said supply means comprise lan annular port between said first and second annular channel means, and having Ian inner peripheral discharge edge portion, and means for feeding CO2 into said port for delivery in said zone of mutual impact of said countercurrent streams, with the addition of rotary scraper means turnable about the axis of said Vchannel means and cooperating with said discharge edge portion of said port. Y

7. Apparatus for the carbonation treatment of sugar juice by the reaction of lime with CO2, which comprises an upright vessel arranged for upward ow of juice therethrough;

means for introducing said juice into said vessel, comprising at least a lower horizontal annular shelf, an upper annular shelf spaced upwardly from said lower shelf, and intermediate .annular shelf means defining with said upper and lower shelves a pair of coaxial annular channel means horizontally sur- -roundin-g a mixing zone, said upper and lower shelves and said intermediate shelf means being connected at their outer peripheries to the vessel wall;

feed conduit means disposed externally of said annular channel means .and communicating with respective annular channel means for simultaneously and tangentially feeding juice into respective channel means in respective opposite directions, whereby the directional iiow energy of the countercurrent streams in said channel means is converted into random turbulence in said mixing zone;

an annular duct associated with said intermediate shelf means substantially concentric therewith;

and supply means for feeding CO2 into said .annular port for delivery substantially in said zone of mutual impact of said countercurrent streams.

8. Apparatus according to claim 7, wherein said annular duct has an inner peripheral discharge opening, with the addition of rotary scraper means turnable about the axis 0f Said channel means, and Acoopera-ting with said discharge opening. i

9. A mixing device which comprises atleast a first and a second coaxial annular channel means in juxtaposition relative to each other and inwardly open and surrounding a mixing zone;

feed conduitfmeans for simultaneously feeding a liquid into respective channel means in respective opposite directions, whereby the directional flow energy; of the countercurrent streams in said channel means is converted into random turbulence in said mixing zone;

supply means for introducing another fluid into said mixing zone, arranged for delivering said other fluid substantially in the zone of mutual impact of said countercurrent Streams, at the inner periphery of said channel means.

10. The mixing device according to claim 9, wherein said supply means comprise a pair of annular shelvesdefining between them an annular port and also defining said annular channel means relative to one another.

11. The mixing device vaccording to claim 9, wherein said annular channel means relative to one another, and wherein a substantially annular supply header is pro-v vided surrounding sad channel means and communicating with said -annular port. 13. The method of mixing a liquid with another fluid, Iwhich comprises,

maintaining one continuously fed stream of liquid in one direction along an annular path, maintaining another continuously lfed stream of liquid along a` separate annular path in the opposite direction, f maintaining said opposedly directed streams adjacent to each other substantially about a common axis, simultaneously discharging the liquids of the respective countercurrent streams toward said axis into a transverse zone of shear between the liquids of the two opposedly directed streams, whereby the directional ow energy of the streams is converted into random turbulence in said zone, while axially displacing the liquid from said zone by saidv continuously fed streams, and introduc-ing said other fluid substantially in the zone of mutual impact of said countercur'rent streams at the inner periphery of said channel means.

References Cited ,ibythe Examiner UNITED STATES PATENTS 630,506 8/1899 Hirzel 261 79.1 1,253,766 1/1918 Alden 2614/9.; 2,377,634 6/1945 Kidd 127-12 3,006,474 10/1961 Fitch 21o- 304 MORRIS O. WOLK, Primary Examiner. 

1. APPARATUS FOR THE CARBONATION TREATMENT OF SUGAR JUICE BY THE REACTION OF LIME WITH CO2, WHICH COMPRISES A VESSEL ARRANGED FOR CONTINUOUS UPWARD FLOW OF JUICE THERETHROUGH; MEANS FOR INTRODUCING SAID JUICE INTO SAID VESSEL, COMPRISING AT LEAST A FIRST AND SECOND COAXIAL ANNULAR CHANNEL MEANS IN JUXTAPOSITION RELATIVE TO EACH OTHER AND INWARDLY OPEN AND HORIZONTALLY SURROUNDING A MIXING ZONE AND LOCATED IN THE LOWER END PORTION OF SAID VESSEL; FEED CONDUIT MEANS FOR SIMULTANEOUSLY FEEDING JUICE INTO RESPECITVE CHANNEL MEANS IN RESPECTIVE OPPOSITE DIRECTIONS, WHEREBY THE DIRECTIONAL FLOW ENERGY OF THE COUNTERCURRENT STEAMS IN SAID CHANNEL MEANS IS CONVERTED INTO RANDOM TURBULENCE IN SAID MIXING ZONE; AND SUPPLYING DUCT MEANS FOR INTRODUCING CO2 INTO SAID MIXING ZONE AND ARRANGED FOR DELIVERLING SAID CO2 SUBSTANTIALLY IN THE ZONE OF MUTUAL IMPACT OF SAID COUNTERCURRENT STREAMS, AT THE INNER PERIPHERY OF SAID CHANNEL MEANS. 